6(1, 


W  ITFrCOMPLTMENTS 


Blood  Pressure  and  Pulse  Rate 

AS  INFLUENCED  BY  DIFFERENT 
POSITIONS  OF  THE  BODY 


Read  at  the  Fifty-fifth  Annual  Session  of  the 
American  Medical  Association ,  in  the  Section 
on  Pathology  and  Physiology ,  and  approved  for 
publication  by  the  Executive  Committee:  Drs. 
V.  C.  Vaughan ,  Frank  B.  Wynn  and  Joseph 
McFarland 


O.  Z.  STEPHENS,  A.M.,  M.D., 


Department  of  Physiology,  Northwestern  University  Medical  School 


Chicago 


Reprinted  from  The  Journal  of  the  American  Medical 
Association ,  October  1,  190 J,. 


CEIICAGO  : 

PRESS  OF  AMERICAN  MEDICAL.  ASSOCIATION 
ONE  HUNDRED  AND  THREE  DEARRORN  AVENUE. 


1904. 


REMOTE  STORA 


BLOOD  PRESSURE  AND  PULSE  RATE. 

AS  INFLUENCED  BY  DIFFERENT  POSITIONS  OF  THE  BODY. 


0.  Z.  STEPHENS,  A.M.,  M.D. 

Department  of  Physiology,  Northwestern  University  Medical  School. 
CHICAGO. 


HISTORY. 

The  blood  pressure  in  the  arteries  was  first  meas¬ 
ured  with  some  degree  of  accuracy  by  Stephen  Hales 
in  1733.  He  ordered  a  mare  to  be  tied  down  on  her 
back,  into  whose  crural  artery,  about  three  inches  from 
her  belly,  he  inserted  a  brass  pipe  one-sixth  inch  in 
diameter.  To  this  pipe,  by  means  of  another  brass 
pipe,  he  fastened  a  glass  tube  9  feet  long,  and  of  nearly 
the  same  diameter  as  the  pipe  in  the  artery.  He  then 
untied  the  ligature  on  the  crural  artery,  as  a  result  of 
which  the  blood  rose  8  feet  3  inches  above  the  level  of 
the  ventricle  of  the  heart.1 

While  blood  pressure  can  be  measured  in  this  way 
with  some  degree  of  accuracy,  there  are  several  objec¬ 
tions  to  the  method,  chief  among  which  are  the  follow¬ 
ing:  1,  Through  the  uncomfortable  position  of  the  ani¬ 
mal  and  the  consequent  effect  on  the  vasomotor  nerve 
fibers,  the  pressure  is  likely  not  to  be  the  same  as  it 
would  under  normal  conditions;  2,  the  inaccuracy  due 
to  the  speedy  coagulation  of  the  blood;  3,  the  clumsi¬ 
ness  and  inconvenience  of  the  apparatus. 

Poiseuille,  many  years  later,  improved  this  method 
of  Hales  by  substituting  for  the  glass  tube  a  mercurial 
manometer.  The  tube  connecting  this  manometer  with 
the  artery  was  filled  with  a  solution  of  sodium  carbon¬ 
ate  to  prevent  coagulation  of  the  blood.2 

Later,  Ludwig  made  an  improvement  on  Poiseuille’s 
mercurial  manometer  by  placing  on  the  mercurial  col¬ 
umn  a  float  carrying  a  writing  style,  by  means  of  which 

1.  “Statistical  Essays,”  vol.  11,  after  Hlll-Schafer’s  Text-book 
of  Physiol.,  1900,  vol.  II. 

2.  “Rech.  sur  la  force  du  coeur  aortique.”  Th&se,  Paris,  1828, 
after  Hill-Schfifer’s  Text-book  of  Physiol.,  1900,  vol.  11. 


p 1 5  * o5 


2 


records  of  the  variation  in  pressure  could  be  taken  on 
revolving  drums.  By  means  of  the  apparatus  a  fair 
degree  of  accuracy  can  be  obtained,  but  the  oscillations 
of  the  mercurial  column,  due  to  inertia,  render  it  ob¬ 
jectionable.  The  mercurial  manometer,  however,  has 
been  used  very  extensively  and  with  very  valuable  re¬ 
sults. 

Piorry,  a  noted  French  physician,  was  one  of  the 
first  to  observe  the  effect  of  the  force  of  gravity  on  the 
circulation,  i.  e.,  the  effect  of  the  change  of  position 
on  the  blood  pressure.  His  observations,  however,  were 
clinical.  Having  been  called  to  a  patient  who  had 
lost  consciousness,  and  who  was  being  supported  in  a 
sitting  position  by  his  friends,  he  placed  him  in  a  hori¬ 
zontal  position,  after  which  the  patient  at  once  re¬ 
gained  consciousness.  Hill  has  also  found,  through  a 
trephine  hole  in  the  skull,  that  the  intracranial  pressure 
is  negative  in  the  sitting  posture  and  positive  when  the 
head  was  bent  down  toward  the  knees.3 

Many  other  observations  of  the  same  nature  have  been 
observed  clinically  on  the  human  subject  and  experi¬ 
mentally  on  the  lower  animals. 

Most  of  the  work  on  the  lower  animals  has  been  done 
by  inserting  a  cannula  connected  with  a  mercurial 
manometer  into  the  carotid  or  femoral  artery,  and  then 
shifting  the  animal  from  one  position  to  another,  about 
a  horizontal  axis  which  passes  through  the  point  of  in¬ 
sertion  of  the  cannula.  In  this  way,  quite  accurate  re¬ 
sults  have  been  obtained.  Of  course  the  animals  were 
invariably  narcotized  or  anesthetized. 

So  far  as  we  have  been  able  to  learn  the  experimental 
observations  on  blood  pressure  in  different  positions  of 
the  body  have  been  confined  to  the  horizontal,  vertical 
feet-down  and  vertical  feet-up  positions.  The  same  is 
true  of  the  pulse  rale.  The  clinical  observations  have 
been  confined  to  the  horizontal,  head-up  and  head-down 
at  no  particular  angle. 

Since  the  advent  of  the  sphygmomanometer,  experi¬ 
ments  have  been  performed  on  the  healthy  human  sub¬ 
ject  in  the  standing,  sitting  and  horizontal  postures. 

The  pulse  rate  in  the  human  subject  in  different  po¬ 
sitions  of  the  body,  so  far  as  we  have  been  able  to  learn,  * 
was  first  studied  by  Guy,4  who  made  observations  on 

3.  Hill :  Journal  Physiol..  Cambridge  and  London,  1885,  rol.  ^ 

xvlli,  p.  15. 


3 


100  men,  averaging  27  years  of  age,  in  the  standing,  sit¬ 
ting  and  lying  positions.  He  found  the  pulse  rate  to 
be  highest  in  the  standing,  lower  in  the  sitting  and  low¬ 
est  in  the  lying  positions. 

We  see,  then,  that  the  subjects  of  blood  pressure  and 
pulse  rate  in  different  positions  of  the  body  are  not 
new  ones;  that  some  of  the  apparatus  used  in  getting 
blood  pressure  was  inaccurate;  that  experimental  ob¬ 
servations  were  on  narcotized  or  anesthetized  animals; 
that  clinical  observations  on  blood  pressure  in  the  dif¬ 
ferent  positions  of  the  body  are  confirmatory  of  the 
experimental  observations. 

In  our  work  on  blood  pressure  we  have  dealt  with  the 
subject  in  a  different  manner,  in  some  respects,  from  our 
predecessors,  insomuch  as  we  have  chosen  more  posi¬ 
tions  of  the  body  and  have  taken  the  pressure  on  both 
sides  of  the  body  in  each  position. 

METHOD. 

(a)  Subjects. — The  subjects  used  in  these  experiments 
were  twenty-two  male  medical  students,  with  an  aver¬ 
age  age  of  24  years  and  an  average  height  of  170  cm. 
In  one  of  these  subjects,  however,  the  pulse  rate  was 
not  obtained,  hence  only  twenty-one  are  used  in  mak¬ 
ing  computations  on  pulse  rate.  In  changing  from 
one  position  to  another,  they  were  allowed  to  remain 
long  enough  in  the  new  position  for  the  circulatory  ap¬ 
paratus  to  become  adjusted  to  the  new  conditions  before 
observations,  either  on  blood  pressure  or  pulse  rate, 
were  taken.  Every  means  was  taken  to  keep  them 
comfortable  and  to  avoid  anything  which  would  tend 
to  provoke  excitement  or  muscular  effort.  The  rate 
of  respiration  was  also  kept  normal. 

( b )  Apparatus. — The  instrument  used  in  taking  the 
blood  pressure  was  the  Riva  Rocci  sphygmomanometer, 
as  modified  by  H.  W.  Cook.  The  instrument  is  now 
so  well  known  among  physiologists  that  a  description  of 
it  here  is  not  demanded. 

( c )  Technic. — Each  of  the  twenty-two  men  were  taken 
through  the  following  positions:  1,  Standing;  2,  sit¬ 
ting;  3,  supine;  4,  head  down  at  an  angle  of  45  de¬ 
grees;  5,  right  lateral;  6,  left  lateral. 

The  blood  pressure  was  taken  in  both  brachial  ar- 


4.  Hill-Schafer’s  Text-book  of  Physiol.,  1900,  vol.  li. 


4 


teries  in  each  position  by  placing  the  band  of  the  in¬ 
strument  around  the  upper  arm  midway  between  the 
elbow  and  shoulder. 

The  pulse  rate  was  also  taken  in  each  position,  the 
count  being  taken  through  a  whole  minute  of  time. 

In  taking  the  pressure  in  the  standing  position,  the 
patient  stood  erect,  the  upper  arm  was  abducted  to  the 


Fig.  1. — Standing. 

horizontal  plane  and  the  forearm  flexed  at  right  angles 
to  the  brachium  and  held  perpendicularly,  with  the 
hand  uppermost.  The  arm  was  supported  in  this  po¬ 
sition  by  an  assistant  in  order  to  relieve  the  subject  of 
any  muscular  effort  in  sustaining  the  arm  himself.  The 
opposite  arm  was  allowed  to  hang  laxly  by  the  side. 

In  the  sitting  position,  the  subject  sat  on  a  stool, 


with  the  thighs  parallel  and  flexed  at  right  angles  to 
the  axis  of  the  body.  The  legs  were  flexed  at  right 
angles  to  the  thighs.  The  arm  in  which  the  pressure 
was  taken  was  held  in  the  same  position  in  relation  to 
the  body,  as  it  was  in  the  standing  posture  (the  assist¬ 
ant  supporting  it),  while  the  hand  of  the  opposite  arm 
lay  laxly  on  the  thigh  of  the  same  side. 


Fig.  2.— Sitting. 

The  subject  in  the  supine  posture  lay  flat  on  his  back 
with  legs  parallel,  and  the  arm  on  the  opposite  side 
to  the  one  in  which  the  pressure  was  taken  lay  parallel 
with  and  along  side  of  the  body.  The  arm  in  which 
the  pressure  was  taken  was  abducted  to  right  angles 
with  the  body  axis,  and  the  forearm  at  right  angles  to 
the  brachium  and  held  perpendicularly.  Thus  it  is 


6 


seen  that  the  arm  did  not  take  the  exact  relation  to 
the  body  in  this  position  that  it  did  in  the  standing 
and  sitting  postures.  In  the  latter,  the  brachium  was 
so  rotated  that  the  inner  aspect  faced  forward,  while 
in  this  position  the  inner  aspect  of  the  brachium  faced 
toward  the  feet,  having  rotated  through  an  arc  of  90 
degrees.  The  variation  in  blood  pressure,  due  to  this 
slight  difference  in  the  relative  position  of  the  arm,  if 
there  be  any  variation  at  all,  would  certainly  be  too 
insignificant  to  be  taken  into  account. 

The  subject  in  the  head-down  position  was  placed  on 
a  table  on  his  back,  around  his  ankles  were  placed  com¬ 
fortable  straps,  which  were  fastened  to  one  end  of  the 
table.  The  end  of  the  table  was  then  elevated  so  that 
the  subject  hung  with  his  head  down,  at  an  angle  of  45 
degrees.  The  arms  assumed  practically  the  same  posi¬ 
tion,  in  relation  to  the  body,  as  they  did  in  the  supine 
position,  the  forearm  of  the  arm  operated  on  being 
held  perpendicularly,  and  the  opposite  arm  lying  along 
side  of  the  body. 

In  the  right  lateral  position  our  subject  lay  on  the 
right  side,  the  head  raised  to  the  horizontal  level  by  a 
pillow,  the  legs  parallel  and  straight,  and  the  left  arm 
parallel  with  and  on  the  body.  The  right  arm  was  ex¬ 
tended  anteriorly  at  right  angles  to  the  body  axis,  the 
forearm  flexed  at  right  angles  to  the  upper  arm  and 
held  perpendicularly  when  the  pressure  was  taken  in 
this  arm.  When  the  pressure  was  taken  in  the  left 
arm  in  this  posture,  the  right  arm  was  allowed  to  as¬ 
sume  a  position  most  comfortable  to  the  subject,  in  or¬ 
der  to  obviate  any  nervous  influence  on  the  circulation 
which  might  arise  from  the  subject  being  uncomfortable. 
The  left  arm  assumed  the  same  relation  to  the  body  as 
it  did  in  the  supine  when  the  pressure  was  taken  in  it. 
This,  of  course,  put  the  forearm  in  a  horizontal  plane. 

The  left  lateral  position  is  a  repetition  of  the  right 
lateral  in  reversed  order,  and  need  not  be  detailed  fur¬ 
ther. 

RESULTS. 

After  the  pressure  in  each  brachial  was  taken  in 
a  given  position,  the  two  results  were  averaged  to  obtain 
a  mean  pressure  in  that  position.  The  results  of  such 
observations,  together  with  the  pulse  rate,  are  shown 
in  the  following  table: 


7 


No. 

Stand¬ 

ing. 

Sitting. 

Supine. 

Head- 

down. 

Right 

Lateral. 

Left 

Lai. 

1  Right  arm  .  . 

.  .  134 

142 

174 

185 

172 

125 

Left  arm  . , 

.  .  122 

132 

150 

174 

124 

163 

Pulse  rate  . 

.  .  97 

90 

72 

69 

68 

72 

2  Right  arm  . 

.  .  146 

153 

163 

170 

157 

119 

Left  arm  .  . 

.  .  146 

153 

155 

171 

118 

158 

Pulse  rate  . 

.  .  85 

81 

64 

57 

59 

63 

3  Right  arm  . 

.  .  106 

115 

128 

137 

126 

81 

Left  arm  . . 

.  .  117 

120 

134 

153 

94 

133 

Pulse  rate  . 

.  .  70 

57 

53 

50 

56 

58 

4  Right  arm  . 

.  .  134 

146 

177 

199 

193 

135 

Left  arm  .  . 

.  .  131 

145 

158 

179 

128 

192 

Pulse  rate  . 

.  .  93 

87 

83 

87 

84 

78 

5  Right  arm  . 

.  .  110 

113 

140 

148 

132 

93 

Left  arm  .  . 

.  .  112 

123 

138 

147 

99 

133 

Pulse  rate  . 

.  .  102 

88 

77 

79 

80 

79 

6  Right  arm  . 

.  .  133 

143 

157 

159 

140 

108 

Left  arm  . . 

.  .  136 

138 

159 

151 

111 

170 

Pulse  rate  . 

.  .  118 

93 

71 

71 

88 

78 

7  Right  arm  . 

.  .  151 

154 

179 

216 

186 

141 

Left  arm  .  . 

.  .  155 

171 

186 

240 

147 

213 

Pulse  rate  . 

.  .  86 

81 

71 

64 

69 

63 

8  Right  arm  . 

.  .  124 

127 

140 

143 

150 

108 

Left  arm  .  . 

.  .  102 

107 

145 

193 

115 

145 

Pulse  rate  . 

.  . . 

.  .  . 

9  Right  arm  . 

1.27 

3.29 

i.34 

148 

144 

92 

Left  arm  .  . 

.  .  114 

118 

130 

136 

96 

134 

Pulse  rate  . 

.  .  86 

78 

64 

65 

74 

70 

10  Right  arm  . 

.  .  115 

130 

138 

159 

129 

116 

Left  arm  . . 

.  .  109 

101 

132 

153 

119 

131 

Pulse  rate  . 

. .  110 

98 

86 

76 

90 

87 

11  Right  arm  . 

.  .  141 

142 

149 

169 

181 

112 

Left  arm  . . 

.  .  139 

135 

149 

165 

122 

151 

Pulse  rate  . 

. .  70 

69 

60 

56 

59 

59 

12  Right  arm  . 

.  .  130 

139 

146 

167 

154 

no 

Left  arm  .  . 

.  .  137 

136 

145 

171 

111 

158 

Pulse  rate  . 

.  .  103 

97 

80 

83 

78 

77 

13  Right  arm  . 

.  .  136 

141 

154 

169 

155 

89 

Left  arm  . . 

.  .  117 

116 

141 

164 

108 

137 

Pulse  rate  . 

.  .  75 

69 

65 

74 

67 

67 

14  Right  arm  . 

.  .  127 

124 

146 

151 

134 

92 

Left  arm  .  . 

.  .  113 

115 

133 

153 

90 

137 

Pulse  rate  . 

.  .  72 

60 

53 

48 

53 

50 

15  Right  arm  . 

.  .  152 

132 

165 

169 

157 

123 

Left  arm  . . 

.  .  134 

137 

156 

168 

122 

153 

Pulse  rate  . 

.  .  83 

81 

76 

73 

77 

75 

1 6  Right  arm  . 

.  .  Ill 

100 

126 

132 

119 

73 

Left  arm  .  . 

.  .  115 

116 

129 

133 

95 

134 

Pulse  rate  . 

.  .  99 

92 

69 

68 

67 

75 

17  Right  arm  . 

.  .  134 

130 

154 

177 

152 

105 

Left  arm  . . 

.  .  125 

141 

161 

184 

110 

157 

Pulse  rate  . 

.  .  71 

70 

62 

58 

59 

58 

18  Right  arm  . 

.  .  164 

152 

170 

203 

195 

135 

Left  arm  .  . 

.  .  156 

161 

178 

218 

134 

198 

Pulse  rate  . 

.  .  92 

84 

74 

76 

77 

75 

19  Right  arm  . 

..  154 

151 

180 

198 

180 

127 

Left  arm  .  . 

.  .  151 

150 

169 

183 

112 

180 

Pulse  rate  . 

.  .  82 

83 

78 

62 

71 

66 

20  Right  arm  . 

.  .  122 

119 

142 

153 

159 

111 

Left  arm  .  . 

.  .  119 

113 

127 

158 

98 

155 

Pulse  rate  . 

.  .  76 

75 

59 

58 

63 

62 

21  Right  arm  . 

..  127 

124 

159 

162 

143 

96 

Left  arm  .  . 

.  .  133 

127 

133 

161 

111 

157 

Pulse  rate  . 

.  .  77 

72 

62 

58 

63 

66 

22  Right  arm  . 

.  .  132 

118 

163 

185 

157 

106 

Left  arm  .  . 

.  .  141 

129 

159 

189 

128 

165 

Pulse  rate  . 

. .  67 

65 

55 

59 

61 

60 

In  summarizing  the  above  data,  we  used  the  Hall- 
Quetelet  method.5  This  method  uses  the  median  value, 


5.  The  Journal  A.  M.  A.,  Dec.  21,  1901. 


8 


instead  of  the  average  or  arithmetical  mean.  The  data 
collected  from  each  individual  are  recorded  on  a  card. 
The  cards  from  the  several  individuals  are  grouped  as 
desired.  We  grouped  our  cards  according  to  the  pulse 
rate  and  blood  pressure  in  each  arm  in  the  different 
positions  of  the  body.  For  illustration,  let  us  take  the 
blood  pressure  in  the  right  arm  in  the  standing  posi¬ 
tion;  and  let  us  take  all  those  cards  showing  a  blood 
pressure  of  105-110  mm.  Hg,  inclusive,  and  place  them 
in  one  group,  and  all  those  showing  a  pressure  of  110- 
115  mm.  Hg  in  another  group,  etc.,  till  we  have  all  the 


Fig.  3. — Supine. 


twenty-two  cards  placed  in  groups,  the  difference  be¬ 
tween  the  minimal  values  of  which  is  5  mm.  Hg  pres¬ 
sure.  We  shall  then  have  the  following  table: 


Table  No.  2. 


Blood 

pressure 

105+ 

110+ 

115+ 

120+ 

125+ 

130+ 

135+ 

140+ 

145+ 

150+ 

155+ 

160+ 

No.  of  ob¬ 
servations 

1 

2 

1 

2 

3 

6 

1 

1 

1 

3 

0 

1 

In  adding  the  number  of  observations  shown  in  the 
table,  we  get  a  total  of  22,  which  corresponds  to  the 
number  of  subjects  in  whom  the  pressure  was  taken. 


9 


The  next  step  is  to  find  the  median  value,  which  Dr. 
Hall  defines  thus:  “The  median  value  is  that  value 
which  is  so  located  in  the  whole  series  of  observations 
of  a  single  measurement  of  a  single  group  that  there 
are  as  many  above  it  as  below  it;  i.  e.,  that  the  num¬ 
ber  of  values  which  it  exceeds  is  equal  to  the  number 
of  values  which  exceed  it.”  Since  the  number  of  obser¬ 
vations  is  22,  the  median  value,  therefore,  will  have  on 
one  side  of  it  11  values,  which  are  less,  and  on  the  other 
side  11  values,  which  are  greater  than  itself.  We  must, 
then,  find  the  eleventh  value.  In  counting  from  left 


Fig.  4. — Head  down. 


to  right,  we  find  that  the  eleventh  value  lies  in  the 
group  130  mm.  Hg,  and  is  the  second  from  the  min¬ 
imal  value  and  fourth  from  the  maximal  value  of  this 
group.  The  median  value,  therefore,  lies  in  this  group, 
which  may  be  called  the  median  group.  We  know, 
then,  that  it  must  be  between  130  mm.  Hg,  the  min¬ 
imal  value  of  the  group,  and  135  mm.  Hg,  the  mini¬ 
mal  value  of  the  next  higher  group.  Now,  according 
to  the  biologic  laws,  the  six  values  in  this  median 
group  will  be  practically  evenly  distributed  throughout 
the  5  mm.  Hg  pressure  between  its  minimal  value  and 
the  minimal  of  the  next  higher  group.  Hence  the  sec- 


10 


ond  value  from  the  left  must  be  130  mm.  Hg  pressure, 
plus  2/6  of  5  mm.  Hg  pressure,  which  equals  131.6  mm. 
Hg,  the  pressure  for  the  right  arm  in  the  standing  po¬ 
sition. 

Dr.  Hall  has  also  reduced  this  process  to  a  mathe¬ 
matical  formula,  thus: 

“Let  n  equal  total  number  of  observations ;  m  equal  the  number 
of  observations  in  the  median  group ;  1  equal  the  sum  of  observa¬ 
tions  to  the  left  of  median  group ;  r  equal  the  sum  to  the  right ; 
a  equal  the  minimum  value  of  the  median  group ;  d  equal  the 
arithmetrical  difference  between  the  minimum  values  of  the 
groups,  and  M  equal  the  median  value  to  be  determined.’’ 

Then 


M=a-t-[d(n-f2— 1)— m] 


d(lH"2-l) 

M=a-f--— = - l 


M=130+ 


5(f- 


:  131 .6  mm.  Hg  pressure  by  substituting  the 
values  of  the  letters  in  the  above  cases. 


In  taking  the  arithmetical  mean,  however,  we  get 
a  pressure  of  132.2  mm.  Hg.  In  observing  tie  table, 
we  see  that  we  have  one  observation  of  quite  high  pres¬ 
sure.  This  slight  increase  of  the  average  over  the 
median  value  is  doubtless  due  to  tins  one  observation. 

In  a  large  number  of  observations  the  dwarf  values 
are  likely  to  balance  the  giant  values,  in  which  case 
the  arithmetical  mean  is  an  accurate  though  time-con¬ 
suming  method  of  evaluating  data.  In  a  small  number 
of  observations,  however,  one  extreme  is  more  certain 
to  overbalance  the  other,  and  in  this  case  the  Hall- 
Quetelet  method  is  the  only  accurate  one.  It  is  also 
accurate  in  handling  large  numbers  and  is  much  sim¬ 
pler  and  more  easily  applied  than  the  old  method. 

Our  data  pertaining  to  the  pulse  rate  and  blood  pres¬ 
sure  in  both  brachial  arteries,  in  the  different  positions 
enumerated  above,  were  handled  in  this  manner,  the 
summary  of  the  results  of  this  evaluation  being  given 
in  the  following  table: 

Table  No.  3. 


Standing. 

Sitting. 

Supine. 

Head 

down. 

Rt  Lat. 

Lt.  Lat. 

Right  arm . 

133.3 

152.5 

166.2 

155 

110 

Average .  . 

131.7 

150.4 

165.6 

134.5i 

133 

Left  arm . 

130 

130 

148.3 

165 

114 

156 

Pulse  rate . 

86 

82 

68.7 

65.8 

68.1 

69.1 

11 


DISCUSSION  OF  EFFECTS  ON  BLOOD  PRESSURE. 

In  scanning  this  table,  it  is  seen  that  the  average 
blood  pressure  in  the  two  arms  increases  in  the  stand¬ 
ing,  sitting,  supine  and  head-down  positions,  respect¬ 
ively,  while  the  pulse  rate  decreases.  It  has  been  con¬ 
sidered  that  the  blood  pressure  varies  as  the  heart  rate, 
times  the  heart  strength  times  the  resistance. 

Expressed  in  terms  of  a  formula,  we  have  P  varies  as 
Hr  X  Hs  X  R,  where  P  equals  blood  pressure,  Hr,  the 
heart  rate,  Hs  the  heart  strength,  and  R  the  resistance. 

This  resistance  may  be  due  to  arterial  causes — arte¬ 
rial  resistance;  it  may  be  due  to  the  capillaries — capil¬ 
lary  resistance;  it  may  be  due  to  contractions  of  the 
arterioles — peripheral  resistance;  it  may  be  due  to 
venous  causes — venous  resistance;  or  it  may  be  due  to 
the  effect  of  gravity  on  the  circulation — hydrostatic  re¬ 
sistance. 

How,  it  remains  to  be  seen  whether  the  phenomena 
observed  in  Table  3  can  be  explained  by  means  of  this 
formula. 

Standing  Position. — We  see  that  the  average  blood 
pressure  in  the  standing  position  is  lower  and  the  pulse 
rate  is  higher  than  in  any  other  position  in  the  series. 
Here  the  current  meets  with  the  least  arterial  and  hy¬ 
drostatic  resistance  on  the  arterial  side  of  the  circula¬ 
tion,  and  with  the  greatest  hydrostatic  resistance  on  the 
venous  side.  Both  of  these  factors  tend  to  decrease  the 
pressure  in  the  upper  portions  of  the  body  by  tending 
to  allow  the  accumulation  of  blood  in  the  lower  portions 
oT  the  circulatory  system.  This  is  partially  compen¬ 
sated  for,  however,  by  the  abdominal  muscles  and  con¬ 
traction  of  the  arterioles  in  the  splanchnic  area.3 

Sitting  Position. — The  average  pressure  in  the  sitting 
position  is  nearly  1  mm.  Hg.  greater  than  in  the  stand¬ 
ing  position,  a  difference  almost  so  slight  in  itself  as  to 
be  ignored.  But  when  we  observe  that  the  pulse  rate 
in  this  position  has  decreased  four  beats  to  the  minute, 
more  importance  attaches  to  this  slight  rise  in  pres¬ 
sure,  and  we  begin  to  wonder  why  the  pressure  did  not 
sink  with  the  lowering  of  the  heart  rate. 

According  to  the  formula,  P  will  vary  with  Hr  where 
Hs  and  R  remain  constant.  Therefore,  if  Hr  decreases, 
P  will  decrease  also.  If  P  does  not  decrease  when  Hr 
decreases,  but,  on  the  contrary,  remains  constant  or 
increases,  it  is  evident  that  the  variation  of  Hr  is  coun- 


12 


terbalanced  or  more  than  counterbalanced  by  the  varia¬ 
tion  of  either  Hs  or  R,  or  both,  in  an  opposite  direction. 
Can  we  account  in  any  way  for  a  sufficient  rise  in  Hs  or 
R,  or  both,  to  produce  the  slight  rise  of  P  against  the 
decrease  in  Hr? 

It  will  be  recalled  that  in  the  sitting  position  the 
thighs  were  flexed  at  right  angles  to  the  body  axis,  and 
the  legs  at  right  angles  to  the  thighs;  that  the  body 
was  sustained  erect  on  the  pelvis,  and  the  hand  of  the 
arm  not  being  operated  on  was  lying  relaxed  on  the 
thigh  of  the  same  side.  The  blood,  then,  must  take  a 
somewhat  different  course  in  this  position  from  what  it 
took  in  the  standing  position,  i.  e.,  it  must  course 
around  two  right  angles  in  each  leg — one  at  the  in¬ 
guinal  region  and  one  at  the  knee.  It  also  deviates 
slightly  from  a  straight  line  at  the  elbow  of  the  arm  not 
being  operated  on.  Thus  the  blood  in  two  of  the  largest 
arteries  turns  two  right  angles  in  each  lower  extremity, 
and  one  large  artery  turns  an  angle  of  approximately 
45  degrees  at  the  elbow.  The  same  is  true  of  the  veins 
in  the  same  localities.  This  introduces  an  arterial  and 
venous  resistance  which  did  not  exist  in  the  standing 
position. 

It  is  possible,  too,  that  the  capillary  resistance  may 
be  increased  by  compression  of  the  gluteal  region  and 
upper  part  of  the  thigh  by  the  weight  of  the  body  on 
them. 

It  has  been  stated  that  through  the  influence  of  the 
vasodilator  nerve  fibers  the  flow  of  blood  to  a  contract¬ 
ing  muscle  is  increased.6  If  this  be  true,  the  flow  of 
blood  to  the  muscles  of  the  lower  extremities  will  be 
increased  while  the  muscles  are  contracting  to  main¬ 
tain  the  body  in  a  standing  position.  This  increased 
flow  of  blood  to  the  lower  portions  of  the  circulatory 
system  will  tend  to  raise  the  pressure  here  and  lower  it 
in  other  portions  of  the  arterial  system. 

The  relaxation  of  these  muscles  in  the  sitting  posi¬ 
tion,  however,  with  practically  the  same  tension  of  the 
abdominal  muscles  and  the  muscles  of  the  back  in  main¬ 
taining  the  trunk  erect  on  the  pelvis,  prevents  the  in¬ 
crease  of  flow  of  blood  to  the  lower  extremities,  which  re¬ 
sults  in  higher  pressure  in  the  rest  of  the  arterial  sys¬ 
tem,  i.  e.,  the  peripheral  or  arteriolar  resistance  is  in¬ 
creased  in  this  position. 


6.  Stewart :  Manual  of  Physiol.,  1900,  p.  153. 


13 


The  force  of  gravity  also  plays  an  important  role. 
In  a  man  6  feet  high  the  hydrostatic  pressure  of  a  col¬ 
umn  of  blood  reaching  from  the  vertex  to  the  sole  of 
the  foot  is  equal  to  140  mm.  Hg,  and  from  the  vertex 
to  the  middle  of  the  abdomen  about  50  mm.  Hg.2  If 
this  statement  be  true,  the  hydrostatic  pressure  in  a 
man  5  feet  8  inches  high — the  average  height  of  our  22 
subjects — will  be  about  134  mm.  Hg.  Now,  if  the  av¬ 
erage  distance  from  the  bend  of  the  femoral  artery  in 
the  inguinal  region  to  the  bend  of  popliteal  behind  the 
knee  be  about  40  cm.,  the  hydrostatic  pressure  in  this 


Fig.  5. — Right  lateral,  lower  arm. 

position  will  not  be  134  mm.  Hg  by  31.5  mm.  Hg, 
the  pressure  of  a  column  of  40  cm.  There  will  be  40 
cm.  of  the  column  of  170  c.m  (5  feet  8  inches),  on 
which  gravity  exerts  a  pressure  downward  on  only  the 
lower  wall  of  the  vessel.  This  column  of  40  cm.  of 
blood,  meeting  resistance  to  its  downward  tendency,  has 
Ho  effect  through  its  own  weight  in  the  column  in  the 
leg  below  it  as  it  had  in  the  standing  position,  but  tends 
to  check  the  flow  of  the  column  above.  The  latter,  by 
its  own  weight  or  hydrostatic  resistance,  and  the  elas¬ 
tic  force  of  the  arteries  must  sweep  this  40  cm.  of 


14 


blood  through  a  horizontal  distance  of  40  cm.  In 
overcoming  this  extra  hydrostatic  resistance,  the  col¬ 
umn  above  must  necessarily  experience  a  rise  in  pres¬ 
sure.  Thus  the  decrease  in  the  hydrostatic  resistance 
due  to  the  decrease  in  height  of  the  column  of  blood, 
is  reacted  on  by  the  increased  pressure  due  to  the  hy¬ 
drostatic  resistance  of  the  40  cm.  to  be  moved  in  a 
horizontal  plane.  This  is  true  on  both  the  arterial  and 
venous  sides  of  the  circulatory  system.  Whether  or  not 
these  two  factors  balance  we  do  not  know.  However, 
to  summarize,  we  see  that  we  have  an  increase  in  the 
arterial,  venous,  capillary  and  peripheral  resistances, 
and  also  the  hydrostatic  resistance  due  to  the  hori¬ 
zontal  column  of  blood.  We  also  have  a  decrease 
in  the  hydrostatic  resistance  due  to  a  decrease  in  height 
of  the  blood  column. 

Now,  since  we  have  an  increase  in  P  and  decrease  in  Hr, 
it  is  evident  that  the  increasing  factors  of  R  must  more 
than  counterbalance  the  decreasing  factor,  since  the 
respiration  was  kept  normal  and  all  nervous  stimuli 
avoided  which  would  tend  to  increase  Hs.  This  in¬ 
creased  pressure  is  shared  by  the  coronary  arteries,  in 
consequence  of  which  an  increase  of  nutriment  is  car¬ 
ried  to  and  increased  tension  placed  on  the  heart  mus¬ 
cle,  both  of  which  tend  to  increase  the  heart  strength.7 

It  is  clear,  then,  that  the  total  increase  in  P  is  not 
due  alone  to  the  increased  resistance,  but  is  brought 
about  partially  by  the  increase  in  the  heart  strength. 
This  increase  of  the  heart  strength,  however,  results 
from  the  increased  pressure  due  to  the  increased  re¬ 
sistance.  Just  what  proportion  of  the  total  increase  in 
P  is  due  to  the  increase  in  R,  and  what  proportion  is 
due  to  the  increase  in  Hs,  we  do  not  know.  We  con- 
;  elude,  therefore,  that  the  increased  blood  pressure  in 
the  brachials  in  the  sitting  position  over  that  in  the 
standing  position  is  due  to  an  increase  in  both  the  re¬ 
sistance  and  the  heart  strength. 

Supine. — In  referring  to  Table  3,  the  median  pres¬ 
sure  in  the  supine  position  is  seen  to  be  150.4  mm.  Hg, 
a  distinct  rise  over  that  in  the  two  previous  positions. 
We  see,  also,  that  the  pulse  rate  has  decreased  to  68.7 
beats  per  minute,  a  distinct  decrease  below  that  in  the 
two  previous  positions.  Therefore,  since  P  is  higher  and 


7.  Roy  and  Adami :  Philosophical  Trans,  of  the  Royal  Society, 
1892.  vol.  clxxxiii,  B.,  pp.  90,  262. 


15 


Hr  lower  than  in  the  two  other  positions,  it  is  clear 
that  Hs  or  R,  or  both,  have  made  a  greater  increase. 

Hill  of  London  has  shown  that,  when  the  body  of 
one  of  the  lower  animals  takes  the  vertical  feet-down 
position,  the  blood  pressure  falls  in  the  carotids  and  at 
the  same  time  rises  in  the  femorals.  When  the  body 
resumes  the  horizontal  position  the  pressure  increases 
in  the  carotids  and  decreases  in  the  femorals,  as  com¬ 
pared  with  what  it  was  at  first.  When  the  animal 
is  placed  in  the  vertical  feet-up  position,  the  pressure 
still  further  rises  in  the  carotids  and  falls  in  the  fem¬ 
orals.  These  phenomena  he  attributed  to  the  hydro- 


Fig.  6. — Right  lateral,  upper  arm. 

static  pressure  of  the  blood.  Again,  if  the  phrenic  nerves 
be  divided  when  the  animal  is  in  the  vertical  feet-down 
position,  the  pressure  will  still  further  fall  in  the  caro¬ 
tids  and  rise  in  the  femorals.  Furthermore,  if  a  cru¬ 
cial  incision  be  made  in  the  abdominal  walls,  the  pres¬ 
sure  falls  still  further  in  the  carotids  'and  rises  in  the 
femorals.  These  phenomena,  he  attests,  point  to  a 
compensatory  apparatus  in  the  splanchnic  area  and  the 
abdominal  walls,  Since  compression  of  the  latter  will 
cause  the  pressure  to  rise  in  the  carotids  and  fall  in 
the  femorals.  This  compensatory  apparatus,  he  thinks, 
becomes  more  nearly  complete  in  animals  that  assume 


16 


more  nearly  the  vertical  position  as  their  natural  pos¬ 
ture;  therefore,  more  nearly  complete  in  man.3 

The  clinical  experience  of  Piorry,  cited  above,  and 
of  many  others,  also  shows  the  effect  of  gravity  on  the 
circulation  in  the  supine  position.  When  the  subject 
is  placed  on  his  back  the  blood  which  previously  tended 
to  gravitate  to  a  plane  below  the  heart,  especially  into 
the  spacious  venous  system  of  the  splanchnic  area,  now 
tends  to  become  more  equally  distributed  throughout 
the  circulatory  system,  since  this  system  has  taken  a 
horizontal  position.  This  tends  to  increase  the  hydro¬ 
static  resistance  in  the  plane  of  the  heart  and  above  it, 
through  an  increased  flow  of  blood  to  these  regions  and 
to  lower  it  in  the  planes  below  through  a  correspond¬ 
ingly  decreased  flow  to  those  regions. 

At  the  same  time,  the  hydrostatic  resistance  is  fur¬ 
ther  increased  by  the  blood  in  the  arterial  system  hav¬ 
ing  to  be  moved  along  a  horizontal  plane  at  right  angles 
to  the  force  of  gravity. 

It  is  decreased,  however,  in  the  lower  portions  of  the 
venous  system  by  a  force  equivalent  to  the  difference 
between  that  required  to  raise  the  return  circulation 
to  the  level  of  the  heart,  and  that  required  to  move  it 
through  a  horizontal  plane  throughout  the  venous  sys¬ 
tem.  It  is  increased,  however,  in  the  upper  portions 
of  this  system  through  the  general  tendency  of  the  blood 
to  become  equally  distributed  throughout  the  circula¬ 
tory  system. 

The  increased  hydrostatic  resistance  in  the  circu¬ 
latory  system  tends  to  strengthen  the  heart  beat  by 
increasing  the  nutriment  to  and  the  tension  on  the  heart 
muscle.  This  increased  force  of  the  heart  “may  more 
than  counterbalance  the  increase  in  the  resistance  to 
the  contractions  of  the  left  ventricle  which  that  rise 
introduces,  so  that  the  ventricle  may  contract  more  com¬ 
pletely  than  it  did  before  the  pressure  was  raised.”8 

It  may  be  possible  that  the  capillary  resistance  is 
slightly  increased  in  this  position  by  the  weight  of  the 
body  on  the  tissues  of  the  back ;  this  is  evidently  small, 
as  the  body  rests  largely  on  bony  prominences,  such  as 
the  sacrum,  shoulder  blades,  etc.,  leaving  the  large  mus¬ 
cular  areas  of  the  back  practically  free  from  pressure. 

We  see,  then,  that  there  is  an  increase  in  the  hydro- 

8.  Roy  and  Adami :  Philosophical  Trans,  of  the  Royal  Society, 
1892.  vol.  clxxxiii,  B..  p.  269. 


17 


static  resistance  in  the  arterial  system  and  upper  por¬ 
tions  of  the  venous  system;  that  because  of  this  in¬ 
crease  of  hydrostatic  resistance  the  heart’s  action  is 
strengthened;  that  there  is  a  possible  slight  increase  in 
the  capillary  resistance;  that  there  is  a  decrease  in  hy¬ 
drostatic  resistance  in  the  lower  portions  of  the  venous 
system. 

Now,  since  P  has  increased,  we  are  forced  to  conclude 
that  the  increase  in  Hs  and  R  more  than  counterbalances 
the  decrease  in  R  in  the  lower  venous  system.  Further¬ 
more,  that  the  ultimate  factor  in  bringing  about  the  in¬ 
crease  in  P  in  this  position  is  the  hydrostatic  resistance. 

Head-Down  Position. — Referring  again  to  Table  3, 
it  is  observed  that  the  blood  pressure  in  the  head-down 
position  has  made  a  leap  of  over  15  mm.  Hg  above 
what  it  was  in  the  supine,  being  now  165.6  mm.  Hg. 
It  will  also  be  noticed  that  the  heart  rate  has  been  low¬ 
ered  almost  three  beats  per  minute,  the  rate  now  being 
65.8.  Now,  since  the  pressure  is  the  greatest  and  the 
heart  rate  is  the  lowest  in  this  position,  it  is  evident  that 
the  heart  strength  or  the  resistance,  or  both,  have  ex¬ 
perienced  the  greatest  increase. 

Since  the  man  is  on  an  inclined  plane  with  the  head 
downward,  it  is  clear  that  the  blood  will  tend  to  course 
toward  the  head  through  the  influence  of  gravity.  This 
produces  an  increased  hydrostatic  resistance  in  the  up¬ 
per  portions  of  the  circulatory  system,  which  is  greater 
than  it  was  in  the  supine,  since  gravity  acts  on  an  angle 
of  45  degrees  with  the  course  of  the  blood,  instead  of 
90  degrees.  It  is  also  greater  than  in  the  standing  and 
sitting  postures,  since  in  the  latter  gravity  acts  in  a 
straight  line  with  the  blood  stream  and  tends  to  pull  it 
to  the  opposite  extreme  of  the  circulatory  system. 

The  hydrostatic  resistance  in  this  position  is  equiva¬ 
lent  to  that  of  a  column  of  blood  extending  perpendic¬ 
ularly  between  the  plane  of  the  feet  and  that  of  the 
brachial  artery,  a  distance  of  about  99  cm.,  with  a 
pressure  of  about  78  mm.  Hg. 

According  to  Hill,3  the  increased  hydrostatic  pressure 
in  the  carotids  in  the  vertical  head-down  position  is  par¬ 
tially  compensated  for  by  a  decrease  in  the  resistance 
.in  the  splanchnic  area,  brought  about  through  the  vaso¬ 
dilator  mechanism;  but  this  compensation  is  far  from 
complete. 

The  same  may  be  said  in  regard  to  the  capillary  re- 


18 


sistance  here,  as  was  said  in  case  of  the  supine;  if 
there  be  an  increase  it  must  be  slight. 

The  hydrostatic  pressure,  being  greater  in  the  upper 
portion  of  the  circulatory  system  than  it  was  in  the  pre¬ 
vious  postures,  will  necessarily  be  shared  to  a  greater 
extent  by  the  coronary  arteries,  in  consequence  of  which 
there  will  be  a  greater  increase  of  nutriment  to  the  heart 
muscle.  The  tension  on  the  heart  will  also  be  greater. 
We  conclude,  therefore,  that  the  strength  of  the  heart 
is  greatest  in  this  position. 

Lateral  Positions. — In  Table  3  it  will  be  seen  that 
the  pressure  in  the  right  lateral  position  is  134.5  mm. 
Hg,  and  the  pulse  rate  is  68.1  beats  per  minute ;  in  the 
left  lateral  the  pressure  is  133  mm.  Hg,  and  the  pulse 
rate  69.1  per  minute.  Here  the  same  general  law  holds 
good — that  the  pulse  rate  decreases  as  the  pressure  in¬ 
creases.  But  we  notice  that  the  pulse  rate  approximates 
that  in  the  head-down  position,  while  the  blood  pressure 
approaches  that  in  the  standing  and  sitting  postures, 
i.  e.,  the  pressure  is  lower  compared  with  the  pulse  rate 
than  in  the  other  lying  positions. 

How,  since  the  pulse  rate  is  much  lower  and  the  blood 
pressure  slightly  higher  in  these  positions  than  in  the 
standing  and  sitting  positions,  it  is  manifest  that  both 
the  heart  strength  and  resistance,  or  either  one  of  them, 
must  be  increased  to  a  greater  extent  than  in  the  latter. 
For  convenience  we  shall  take  the  average  pressure  and 
pulse  rate  in  these  positions  in  comparing  them  with  the 
others,  and  later  take  the  two  separately,  in  compar¬ 
ing  them  with  each  other.  The  following  table  will  then 
be  useful : 


Table  No.  4. — Lateral  Positions. 


Right 

Arm. 

Left 

Arm. 

Average. 

Lower 

Arm. 

Upper 

Arm. 

Blood  Pressure . 

Pulse  Rate . 

134.5 

68.1 

133 

69.1 

133.8 

68.6 

155.5 

112 

This  table  shows  the  average  blood  pressure  in  these 
positions  to  be  133.8  mm.  Hg  and  the  average  pulse  rate 
68.6  beats  per  minute.  By  comparing  these  figures  with 
those  in  Table  3  we  see  the  pulse  rate  is  nearly  the  same 
as  in  the  supine,  and  but  slightly  higher  than  in  the 
head-down  positions,  while  the  pressure  is  much  lower. 
That  means  that  the  heart  strength,  the  resistance,  or 
both,  have  decreased. 


19 


How  can  we  account  for  these  phenomena?  In  the 
first  place,  how  can  we  account  for  the  slight  increase  in 
the  pressure  over  the  great  fall  in  the  heart  rate  from 
what  it  was  in  the  standing  and  sitting  positions?  In 
the  latter  a  comparatively  small  amount  of  blood  was 
moved  along  a  horizontal  plane  by  the  heart  force,  thus 
overcoming  the  hydrostatic  resistance  due  to  gravity 
acting  at  right  angles  to  the  blood  current,  while  in  the 
lateral  positions  the  blood  moves  nearly  horizontally 
through  the  entire  circulatory  system. 

Here,  also,  the  blood  tends  to  become  more  equally 
distributed  throughout  the  circulatory  system.  This  re¬ 
sults  in  a  lowered  hydrostatic  resistance  in  the  lower 
portions  of  the  body,  with  a  corresponding  increase  in 
the  upper  portions. 

In  this  position  it  will  be  recalled  that  the  lower  arm 
was  extended  anteriorly  at  right  angles  to  the  body  axis. 
Instead  of  the  blood  passing  from  the  subclavian  artery 
through  the  branchial  in  a  straight  line  to  the  elbow,  it 
deviates  90°  from  this  course  and  passes  directly  for¬ 
ward.  This  offers  a  greater  resistance  to  the  blood  cur¬ 
rent  above,  and  at  the  same  time  tends  to  lessen  the 
pressure  in  the  radial  below  it.  We  conclude,  therefore, 
that  because  of  this  variation  the  systemic  pressure  is 
somewhat  higher  than  is  recorded  in  the  above  table. 
This  is  a  greater  arterial  resistance  than  we  had  in  the 
standing  and  less  than  in  the  sitting  positions.  In  the 
upper  arm  the  forearm  was  horizontal  instead  of  per¬ 
pendicular,  as  it  was  in  the  other  positions,  while  the 
brachium  was  perpendicular  instead  of  horizontal. 
Hence,  these  two  differences  balance.  Because  of  the 
increased  resistance  the  heart  force  is  also  increased  in 
the  same  manner  as  has  been  given  above. 

We  see,  then,  that  the  hydrostatic  resistance  is  greater 
in  the  planes  of  the  heart  and  above  it,  in  these  posi¬ 
tions,  than  in  the  standing  and  sitting  positions;  that 
the  arterial  resistance  is  slightly  greater  than  in  the 
standing,  but  less  than  in  the  sitting  position;  that  the 
heart  strength  is  increased  because  of  the  increased  re¬ 
sistance.  Now,  since  P  is  slightly  higher  and  Hr  much 
lower,  Hs  and  E,  one  or  both,  must  be  much  increased. 

Now,  why  is  the  pressure  lower  than,  and  the  heart 
rate  nearly  the  same  as,  it  was  in  the  supine?  In  the 
latter  the  circulatory  system  lies  practically  in  a  hori¬ 
zontal  plane.  f  n  the  lateral  positions  it  is  “on  edge,”  as  it 


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were,  and  beside,  the  upper  portion  is  slightly  higher  than 
the  lower,  since  the  distance  from  the  central  axis  of 
the  body  to  the  point  of  the  shoulder  is  somewhat  greater 
than  it  is  from  the  same  axis  to  the  most  distant  point 
of  the  crest  of  the  ilium  or  great  trochanter.  This  gives 
a  slightly  inclined  plane,  down  which  the  blood  tends  to 
gravitate  toward  the  feet,  thus  raising  the  pressure  below 
the  heart  and  lessening  it  above,  as  compared  with  what 
it  would  be  in  the  supine  position.  The  resistance,  there¬ 
fore,  being  less,  the  heart  strength  will  be  less  because 
of  lessened  nutrition  to,  and  tension  on,  the  heart  mus¬ 
cle.  The  decrease  in  P,  then,  must  be  due  to  a  decrease 
in  Hs  and  E. 

The  same  things  are  true  in  the  head-down  position 
as  in  the  supine,  but  in  a  more  marked  degree.  Here, 
however,  Hs  has  decreased  to  a  greater  degree ;  hence,  we 
conclude  that  P  has  decreased  as  a  result  of  the  decrease 
in  Hr,  Hs  and  E. 

Now,  Table  4  shows  that  the  average  pressure  is  1.5 
mm.  Hg  greater  and  the  pulse  rate  a  half  beat  less  in  the 
right  than  in  the  left  lateral  position.  How  may  this 
slight  rise  of  pressure  be  explained  ? 

The  aorta  passes  from  the  left  ventricle  upward  and 
slightly  forward  and  to  the  right.  It  then  curves  back¬ 
ward,  upward  and  to  the  left.  Therefore,  in  the  right 
lateral  position  the  heart  lifts  the  greater  portion  of 
blood  against  the  force  of  gravity  to  the  perpendicular 
distance  between  the  planes  of  the  mouth  of  the  ascend¬ 
ing  and  the  beginning  of  the  descending  aorta,  respec¬ 
tively.  It  also  turns  this  blood  through  a  semicircle  in 
its  course  through  the  arch.  In  the  left  lateral  this  re¬ 
sistance  is  absent.  The  force  of  gravity  alone  would  be 
sufficient  to  take  the  blood  around  the  arch  of  the  aorta 
after  it  reaches  the  top  of  the  ascending  portion.  This 
increased  resistance  in  the  right  lateral  in  turn  produces 
a  greater  heart  strength.  It  is  clear,  then,  that  the  in¬ 
crease  in  P  is  due  to  an  increase  in  Hs  and  E. 

DISCUSSION'  OF  EFFECTS  ON  PULSE  RATE. 

“The  mere  fact  that  the  centripetal  fibers  which  call 
the  vagus  into  play  by  reflex  action  come  chiefly  from 
the  heart  itself,  shows  that  one  part,  and  a  very  impor¬ 
tant  part,  of  the  vagus  function  is  to  reduce  the  work 
done  by  the  heart  in  the  interest  of  the  heart  itself.  We 
conclude,  then,  tliat  the  vagus  acts  as  a  protecting  nerve 


21 


to  the  heart,  reducing  the  work  thrown  on  that  organ 
when,  from  fatigue  or  other  causes,  such  relief  is  re¬ 
quired  by  it.  The  fact,  however,  that  there  exists  cen¬ 
tripetal  fibers  which  call  the  vagus  center  into  activity, 
in  such  nerves  as  the  sciatic  and  splanchnic,  shows  that 
the  vagus  mechanism  may  be  called  on  to  act  in  the  in¬ 
terests  of  other  parts  of  the  body  whose  circulation  re¬ 
quires  to  be  diminished.  We  conclude,  therefore,  that 
the  vagus  may  be  used  by  other  parts  of  the  body  to  di¬ 
minish  the  blood  pressure  and  the  output  of  the  heart, 
and  thereby  reduce  the  circulation. 

“Among  the  organs  whose  protection  against  over¬ 
congestion  is  of  the  greatest  importance,  it  need  hardly 
be  said  that  the  central  nervous  system  takes  the  fore¬ 
most  place.  It  is  well  known  that  if  the  intracranial 
pressure  be  raised  artificially  powerful  excitation  of  the 
vagus  center  is  produced.  Vagus  action  also  results  from 
rise  in  the  blood  pressure  in  the  systemic  arteries,  and 
the  excitation  thus  produced  can  be  shown  to  be  due  to 
the  high  pressure  within  the  vessels  of  the  central  nerv¬ 
ous  system  and  not  to  any  direct  effect  of  the  rise  of 
pressure  on  the  heart.  We  must,  therefore,  look  on  the 
vagus  mechanism  as  a  means  by  which  the  central  nerv¬ 
ous  system  gains  protection  against  too  great  congestion. 

“The  dependence  on  the  blood  pressure  of  the  degree  of 
vagus  action,  and  the  readiness  with  which  the  vagus 
center  in  the  medulla  is  called  into  play  by  a  rise  of 
the  intracranial  pressure,  seem  to  us  to  indicate  that  the 
mechanism  in  question  is  especially  employed  in  the 
interests  of  the  central  nervous  system  as  well  as  the 
heart  itself/57 

Now,  if  it  be  true  that  the  vagus  acts  as  a  protecting 
nerve  both  to  the  heart  itself  and  the  central  nervous  sys¬ 
tem,  it  is  clear  that  the  reduced  heart  rate  in  the  various 
positions  of  the  body  in  the  order  named  is  in  response 
to  the  action  of  the  vagus  in  endeavoring  to  protect  the 
heart  and  central  nervous  system  against  the  increasing 
pressure. 

SUMMARY. 

1.  The  blood  pressure  increases  in  the  brachials  from 
the  standing  to  the  head-down  positions,  inclusively,  in 
the  following  order:  Standing,  sitting,  left  lateral,  right 
lateral,  supine  and  head-down. 

2.  The  greater  the  hydrostatic  resistance  in  the  upper 
portions  of  the  circulatory  system  the  greater  the  in- 


22 


crease  in  pressure  where  the  nervous  and  respiratory  sys¬ 
tems  are  kept  normal. 

3.  An  increase  of  resistance  is  accompanied  by  an  in¬ 
crease  in  heart  strength ;  the  strength  of  the  heart,  there¬ 
fore,  will  increase  in  the  different  positions  in  the  fol¬ 
lowing  order:  Standing,  sitting,  left  lateral,  right  lat¬ 
eral,  supine  and  head-down. 

4.  The  pulse  rate  decreases  in  the  same  order  that 
the  blood  pressure  increases. 

5.  The  decrease  in  the  pulse  rate  is  a  conservative  act 
on  the  part  of  nature  to  protect  the  heart  itself  and  the 
central  nervous  system. 


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